Image forming system

ABSTRACT

An image forming system, having means for storing usage histories of latent image carriers, developer, or the like and maintenance cycles of image forming apparatuses and having a function for selecting image forming apparatuses outputting an image based on the usage history data or the maintenance cycles, in order to achieve uniform output image qualities. By managing the usage histories so as to achieve approximately the same deteriorated conditions of the latent image carriers of the image forming apparatuses, the image forming apparatuses can be put in the same condition and thus the output image qualities can be approximately the same in the image forming apparatuses. Additionally, the maintenance cycles can be adjusted to be approximately the same in the image forming apparatuses. Otherwise, maintenance periods can be controlled so as not to overlap in the image forming apparatuses.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an image forming systemcomprising a plurality of image forming apparatuses connected so as tooutput data or to form image copies from selected ones.

[0003] 2. Description of the Prior Arts

[0004] Recently, with the progress of digitalization and networking ofcopying machines, printers, and complex machines caused by the advanceof highly-networked information technology, a technology of an imageforming system capable of obtaining a large number of image copies in ashort time has been in practical use. In the image forming system, anoriginal image read from a certain single image reader is copied at ahigh speed using a plurality of digital copying machines connected toeach other or image data transmitted from a computer are output to aplurality of printers at a high speed.

[0005] For the image forming system in conventionally practical use,importance is attached to a great volume of and high-speed image output.Therefore, there has been proposed a method of forming an imageefficiently by distributing and sharing image output processing (forexample, refer to Japanese Unexamined Patent Publication (Kokai) Nos.Hei 9-261395 (1997) and Hei 11-127290 (1999)). On the other hand, therehas been proposed a method of correcting differences in image qualityamong the image forming apparatuses in Japanese Unexamined PatentPublication (Kokai) No. 2001-83848. Furthermore, there has also beenproposed a method of analyzing received image data and selectingprinters for outputting the image in Japanese Unexamined PatentPublication (Kokai) No. Hei 10-240552 (1998).

[0006] To output an image by using a plurality of image formingapparatuses including a number of copying machines, printers, andcomplex machines connected to each other with the same image quality orwith a desired function (image combine staple, folding, etc.), it isimportant to correct the image quality or to select the function ordevices in consideration of the conditions (a material to be used, afrequency in use, individual differences in devices, etc.) of the imageforming apparatuses and functional differences between the devices.

[0007] The aforementioned conventional image forming system has beenproposed on the assumption that the conditions and functions of theimage forming apparatuses are equivalent. In other words, it is notconsidered in the conventional systems that the image formingapparatuses may be different in conditions or functions. Therefore, theconventional system has a problem that it is hard to standardize theimage quality or the function in image forming apparatuses different inconditions or functions.

SUMMARY OF THE INVENTION

[0008] The present invention has been made in view of the above problem.It is an object of the present invention to provide an image formingsystem capable of outputting an image by means of a plurality of imageforming apparatuses connected to each other, with the same image qualityand desired functions applied in consideration of output conditions orfunctional differences between individual image forming apparatuses.

[0009] To resolve the above problem, there is provided an image formingsystem according to a first aspect of the present invention, comprisingcommunication means for interconnection and a plurality ofelectrophotographic image forming apparatuses each visualizing a latentimage on a latent image carrier generated based on input image data bymeans of developer and transferring it to a recording material, whichare connected via the communication means, the image forming systemhaving means for storing usage histories of the latent image carriers ofthe image forming apparatuses and having a function of selecting imageforming apparatuses outputting the image based on the carrier usagehistory data stored in the storing means.

[0010] The image forming system according to a second aspect of thepresent invention has a feature that the usage history of the latentimage carrier is based on the number of transferred pages obtained withreference to an operating time or recording materials in the firstaspect of the invention.

[0011] The image forming system according to a third aspect of thepresent invention has a feature that the usage history of the latentimage carrier is modified according to a characteristic of deteriorationthrough use of each latent image carrier in the first or second aspectof the invention.

[0012] The image forming system according to a fourth aspect of thepresent invention has a feature that the image forming apparatusesoutputting the image are selected so that the usage histories of thelatent image carriers of the image forming apparatuses are approximatelythe same in one of the first to third-aspects of the invention.

[0013] According to a fifth aspect of the present invention, there isprovided an image forming system, comprising communication means forinterconnection and a plurality of electrophotographic image formingapparatuses each visualizing a latent image on a latent image carriergenerated based on input image data by means of developer andtransferring it to a recording material, which are connected via thecommunication means, the image forming system having means for storingusage histories of the developer of the image forming apparatuses andhaving a function of selecting image forming apparatuses outputting theimage based on the developer usage history data stored in the storingmeans.

[0014] The image forming system according to a sixth aspect of thepresent invention has a feature that the usage history of the developeris based on the number of transferred pages obtained with reference toan operating time of a developing device, which contains the developerand supplies it to the latent image carrier, or recording materials inthe fifth aspect of the invention.

[0015] The image forming system according to a seventh aspect of thepresent invention has a feature that the usage history of the developeris modified according to a characteristic of deterioration through useof the developer in the fifth or sixth aspect of the invention.

[0016] The image forming system according to an eighth aspect of thepresent invention has a feature that the image forming apparatusesoutputting the image are selected so that the usage histories of thedeveloper are approximately the same in the image forming apparatuses inone of the fifth to seventh aspects of the invention.

[0017] According to a ninth aspect of the present invention, there isprovided an image forming system, comprising communication means forinterconnection and a plurality of electrophotographic image formingapparatuses each visualizing a latent image on a latent image carriergenerated based on input image data by means of developer andtransferring it to a recording material, which are connected via thecommunication means, the image forming system having means for storingusage histories after maintenance of the image forming apparatuses andhaving a function of selecting image forming apparatuses outputting theimage based on the aforementioned usage history data.

[0018] The image forming system according to a 10th aspect of thepresent invention has a feature that the usage history after maintenanceis based on the number of transferred pages obtained with reference toan operating time for image formation of the image forming apparatus orrecording materials in the eighth aspect of the invention.

[0019] The image forming system according to an 11th aspect of thepresent invention has a feature that the usage history after maintenanceis modified according to a characteristic of deterioration through useof each image forming apparatus in the ninth or 10th aspect of theinvention.

[0020] The image forming system according to a 12th aspect of thepresent invention has a feature that the image forming apparatusesoutputting the image are selected so that the usage histories aftermaintenance are approximately the same in the image forming apparatusesin one of the ninth to 11th aspects of the invention.

[0021] According to a 13th aspect of the present invention, there isprovided an image forming system, comprising communication means forinterconnection and a plurality of electrophotographic image formingapparatuses each visualizing a latent image on a latent image carriergenerated based on input image data by means of developer andtransferring it to a recording material, which are connected via thecommunication means, the image forming system having means for storinginformation on average photographic densities of developer afterreplacement and having a function of selecting image forming apparatusesoutputting the image based on the average photographic densitiesobtained from the information.

[0022] The image forming system according to a 14th aspect of thepresent invention has a feature that the means for storing theinformation on the average photographic densities includes at leastmeans for storing usage histories of the developer, means forcalculating the photographic densities during image formationsuccessively, and means for calculating the average photographicdensities from the usage histories and the successively calculatedphotographic densities in the 13th aspect of the invention.

[0023] The image forming system according to a 15th aspect of thepresent invention has a feature that the image forming apparatusesoutputting the image are selected so that the average photographicdensities are approximately the same in the image forming apparatuses inthe 13th or 14th aspect of the invention.

[0024] According to a 16th aspect of the present invention, there isprovided an image forming system, comprising communication means forinterconnection and a plurality of electrophotographic image formingapparatuses each visualizing a latent image on a latent image carriergenerated based on input image data by means of developer andtransferring it to a recording material, which are connected via thecommunication means, the image forming system having means for detectingamounts of remaining developer of the image forming apparatuses andmeans for calculating a black ratio of the image data and having afunction of selecting image forming apparatuses outputting the imagebased on the remaining developer amount data and the black ratio data.

[0025] The image forming system according to a 17th aspect of thepresent invention has a feature that the image forming apparatusesoutputting the image are selected so that the amounts of remainingdeveloper after the image formation are approximately the same in theimage forming apparatuses in the 16th aspect of the invention.

[0026] The image forming system according to an 18th aspect of thepresent invention has a feature that the developer contains colorparticles in one of the first to 17th aspects of the invention.

[0027] The image forming system according to a 19th aspect of thepresent invention has a feature that a part or all of the plurality ofimage forming apparatuses connected to each other via the communicationmeans are of different models in one of the first to 18th aspects of theinvention.

[0028] The image forming system according to a 20th aspect of thepresent invention further comprises a display unit for displaying a listof the image forming apparatuses selected for outputting the image inone of the first to 19th aspects of the invention.

[0029] The image forming system according to a 21st aspect of thepresent invention further comprises an operating unit for giving aninstruction to execute the output with specifying a part or all of theimage forming apparatuses displayed on the display unit in the 20thaspect of the invention.

[0030] The image forming system according to a 22nd aspect of thepresent invention further comprises a host device control unit forselecting the image forming apparatuses outputting the image based onone of the aforementioned data in one of the first to 21st aspect of theinvention.

[0031] The image forming system according to a 23rd aspect of thepresent invention has a feature that the host device control unit isincorporated in at least one of the image forming apparatuses in the22nd aspect of the invention.

[0032] The image forming system according to a 24th aspect of thepresent invention has a feature that the host device control unit isconnected to the image forming apparatuses independently of the imageforming apparatuses connected to each other in the 22nd aspect of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a diagram showing a connection of an image formingsystem according to an embodiment of the present invention;

[0034]FIG. 2 is a block diagram showing an image forming apparatusaccording to the embodiment in view of a functional aspect;

[0035]FIG. 3 is a schematic sectional view showing an internal structureof the image forming apparatus according to the embodiment;

[0036]FIG. 4 shows a connection of an image forming system according toanother embodiment of the present invention;

[0037]FIG. 5 is a flowchart showing an example of an output procedure inan image forming system according to an embodiment of the presentinvention;

[0038]FIG. 6 is a flowchart showing an example of an output procedure inan image forming system according to another embodiment of the presentinvention;

[0039]FIG. 7 is a flowchart showing an example of an output procedure inan image forming system according to still another embodiment of thepresent invention;

[0040]FIG. 8 is a flowchart showing an example of an output procedure inan image forming system according to still another embodiment of thepresent invention; and

[0041]FIG. 9 is a flowchart showing an example of an output procedure inan image forming system according to still another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] A preferred embodiment of the present invention will now bedescribed in detail hereinafter with reference to the accompanyingdrawings.

[0043] As shown in FIG. 1, a plurality of image forming apparatuses 1 ton, which are digital complex machines, are connected to each other sothat they can output data via LAN interfaces 1 a to na included therein,respectively, and a LAN 50, and further the LAN 50 is connected to ahost device control computer 30 via a LAN interface 30 a in the imageforming system. In other words, the LAN interfaces 1 a to na arecommunication means for the image forming apparatuses. In thisembodiment, the host device control computer 30 controls the output, andtherefore the host device control computer 30 is provided with a hostdevice control unit 300 for the control. The number of image formingapparatuses in the image forming system can be modified appropriately.

[0044] As shown in a block diagram of FIG. 2 showing the image formingapparatus 1, each image forming apparatus comprises an image formingapparatus control unit 100 as a body of a digital copier, a scanner unit130, an operating unit 140, a printer unit 150, and an image processingcontrol unit 200 for processing image data input from an external devicevia the LAN 50 or for processing image data obtained by the scanner unit130 so that it can be transferred to the external device. The LAN 50 isconnected to a terminal 60 provided as the external device in thisembodiment.

[0045] The image forming apparatus control unit 100 has the LANinterface 1 a connected to the LAN 50 as mentioned above. The LANinterface 1 a is connected to a PCI bus 1 b for connecting the imageforming apparatus control unit 100 to the image processing control unit200 inside the image forming apparatus 1. In the image forming apparatuscontrol unit 100, the PCI bus 1 b is connected to a DRAM control IC 103,and the DRAM control IC 103 is connected to an image memory 106comprising a compressed memory 106 a and a page memory 106 b.

[0046] The image forming apparatus control unit 100 has an apparatuscontrol CPU 101, and the apparatus control CPU 101 is connected to theDRAM control IC 103. Furthermore, the apparatus control CPU 101 isconnected to a nonvolatile memory 102. The nonvolatile memory 102 storesa program for operating the apparatus control CPU 101, print settinginformation of the image forming apparatus 1, machine settinginformation, and the like. The apparatus control CPU 101 can readnonvolatile data stored in the nonvolatile memory 102 and can writedesired data as nonvolatile data into the nonvolatile memory 102. Theapparatus control CPU 101 controls operations of the components of theimage forming apparatus 1 according to the print setting information orthe machine setting information stored in the nonvolatile memory 102.

[0047] The nonvolatile memory 102 can store usage history data of alatent image carrier, usage history data of developer, usage historydata after maintenance, remaining developer amount data, and black ratiodata described later, which can be read out if necessary. The apparatuscontrol CPU 101 can update history data stored in the nonvolatile memory102 in continuing a use of the apparatus and can reset theaforementioned usage history data, remaining amount data, and blackratio data due to replacement of the latent image carrier or developeror due to carrying out the maintenance. In addition, the apparatuscontrol CPU 101 can calculate an average black ratio by using the abovedata and can store the average photographic data into the nonvolatilememory 102. Further, the apparatus control CPU 101 can modify the usagehistory data according to a characteristic of deterioration through useof the apparatus, and it can previously determine a modification datatable or a modification formula for the modification and store it in thenonvolatile memory 102. The apparatus control CPU 101 can modify usagehistory or other data stored in the nonvolatile memory 102 withmodification data whenever referencing it. Furthermore, usage history orother data can be modified with the modification data before storing theusage history or other data into the nonvolatile memory.

[0048] Furthermore, the apparatus control CPU 101 can communicate withother image forming apparatuses and the host device control computer 30via the LAN interface 1 a. Therefore, it can transmit or receive imagedata or image processing instructions to or from these other imageforming apparatuses and the host device control computer 30. Stillfurther the device control CPU 101 can send various usage history data,remaining developer amount data, and average black ratio data storedaccording to a request from the control computer 30 at the time of anoutput.

[0049] Subsequently, the scanner unit 130 has a CCD 131 for performingoptical reading and a scanner controller 132 for controlling the entirescanner unit 130. The scanner controller 132 is connected to the controlCPU 101 so that serial communications are ensured between them. The CCD131 is connected to a read processing unit 104 for processing image dataread by the CCD 131. The read processing unit 104 is connected to acompressor IC 105 for compressing the image data. The compressor IC 105is connected to the aforementioned DRAM control IC 103. The scanner unit130, the read processing unit 104, and the compressor IC 105 form imagereading means.

[0050] The operating unit 140 comprises a touch panel 141 and anoperating unit controller 142, with the touch panel 141 connected to theoperating unit controller 142 and with the operating unit controller 142connected to the device control CPU 101. In the operating unit 140, thetouch panel 141 enables inputs of various settings in the image formingapparatus 1, and various information can be displayed if necessary. Inother words, the touch panel 141 also serves as a display unit. Theinformation input from the touch panel 141 is sent to the apparatuscontrol CPU 101, which then performs predetermined processing.

[0051] Furthermore, the DRAM control IC 103 is connected to adecompressor IC 107 for expanding the compressed image data. Thedecompressor IC 107 is connected to a write processing unit 108. Thewrite processing unit 108 is connected to a laser diode (LD) 151 of theprinter unit 150 and processes data for use in an operation of the LD151. More specifically, it generates control data for controlling the LD151 so as to achieve a latent image based on the image data. The printerunit 150 has a printer controller 152 for controlling the entire printerunit 150, and the printer controller 152 is connected to theaforementioned control CPU 101. Details of the printer unit 150 and thelike will be described later. The PCI bus 1 b is connected to a HDD 109,which is capable of saving image data or the like at user's request.

[0052] The PCI bus 1 b is also connected to a DRAM control IC 201 of theimage processing control unit 200. In the image processing control unit200, the DRAM control IC 201 is connected to an image memory (DRAM) 202,which is an image storage unit. Furthermore, in the image processingcontrol unit 200, a common bus is connected to the DRAM control IC 201,an image processing control CPU 203, and a LAN interface 205. The LANinterface 205 is connected to the LAN 50. An HDD 204 is provided tostore image data or the like as is stored in a nonvolatile storage.

[0053] The following describes a basic operation of the image formingapparatus.

[0054] A procedure for storing image data in the image forming apparatus1 will now be described below.

[0055] First, it is described that the scanner unit 130 reads an imageto generate image data in the image forming apparatus 1. The scannerunit 130 optically reads the image from an original by means of the CCD131. At that time, the scanner controller 132 that receives aninstruction from the apparatus control CPU 101 controls the operation ofthe CCD 131.

[0056] The apparatus control CPU 101 operates according to a program andissues an instruction to the scanner unit 130 on the basis of anoperation of the operating unit 140 or of the terminal 60. The imageread by the CCD 131 is data-processed in the read processing unit 104,and the data-processed image data is compressed by a predeterminedmethod in the compressor IC 105 and stored in the compressed memory 106a via the DRAM control IC 103.

[0057] In other cases, image data is input to the image formingapparatus 1, for example, via the LAN 50 and the LAN interface 205. Theabove image data is, for example, generated by an application program inthe terminal 60. The data is received by the image processing controlunit 200 via the LAN interface 205 and stored once in the image memory202 by means of the DRAM control IC 201. The data in the image memory202 is further stored once in the page memory 106 b via the DRAM controlIC 201, a PCI bus 15, and the DRAM control IC 103. The data stored inthe page memory 106 b is sequentially sent to the compressor IC 105 viathe DRAM control IC 103 and compressed and then stored in the compressedmemory 106 a via the DRAM control IC 103.

[0058] Still further, as another example, image data is transferred viathe LAN 50 and stored in the compressed memory 106 a via the LANinterface 1 a and the DRAM control IC 103 of the image forming apparatus1. The above image data is, for example, generated by reading an imagein image forming apparatuses 2 to n and transmitted via the LAN 50.

[0059] After the image data is stored in the compressed memory 106 a asmentioned above and if the image forming apparatus 1 is used as ascanner, the image data obtained using the scanner unit 130 is sent tothe decompressor IC 107 via the DRAM control IC 103 from the compressedmemory 106 a and the data is expanded. The expanded data is then sent tothe page memory 106 b via the DRAM control IC 103 so as to be stored.The data stored in the page memory 106 b is stored in the image memory202 of the image processing control unit 200 via the DRAM control IC103, the PCI bus 1 b, and the DRAM control IC 201 of the imageprocessing control unit 200.

[0060] The image data stored in the image memory 202 is transmitted tothe terminal 60 or the like via the LAN interface 205 and the LAN 50.

[0061] The image data stored in the compressed memory 106 a can betransmitted to other image forming apparatuses 2 to 6 via the DRAMcontrol IC 103, the LAN interface 1 a, and the LAN 50 according to aninstruction from the apparatus control CPU 101. Other image formingapparatuses 2 to n can receive and store the image data and can furtherperform the image formation.

[0062] If the image is output from the image forming apparatus 1, theimage data is stored into the compressed memory 106 a as mentionedabove, and then it is sent from the compressed memory 106 a to thedecompressor IC 107 via the DRAM control IC 103 to expand the data.Thereafter, the expanded data is sent to the write processing unit 108to write the data into a latent image carrier (described later) in theLD 151. The printer unit 150 receives an instruction from the apparatuscontrol CPU 101 and the printer controller 152 controls respectiveunits. Thereby, the printer unit 150 makes printing on a predeterminedrecording sheet (not shown), which is a recording material. Furthermore,if there is provided a post-processing device, which is not shown inFIG. 2, the post-processing device performs required post-processingupon request of given post-processing (punching, stapling, etc.) anddischarges the sheet.

[0063] Subsequently, the main mechanical structure of the image formingapparatus 1 is described below with reference to FIG. 3, for assistancein explaining an operation of the printer unit 150. In FIG. 3 the samereference numerals have been used as in FIGS. 1 and 2 for similar parts.

[0064] The image forming apparatus 1 comprises original writing units153Y, 153M, 153C, and 153K including an LD 151, photosensitive members16Y, 16M, 16C, and 16K as latent image carriers, charging means 17Y,17M, 17C, and 17K, and developing devices 18Y, 18M, 18C, and 18K.Further, it comprises intermediate transfer units 19Y, 19M, 19C, and19K. The intermediate transfer units 19Y, 19M, 19C, and 19K are woundaround a plurality of rollers, respectively, and supported in arotatable condition. They are provided with an endless-belt typeintermediate transfer member 19 a arranged so that it can be put incontact with the photosensitive members 16Y, 16M, 16C, and 16K andprimary transfer means 19 for transferring an image by putting theintermediate transfer member 19 a in contact with the photosensitivemembers 16Y, 16M, 16C, and 16K. Furthermore, there are arranged cleaningunits 20Y, 20M, 20C, and 20K in the vicinity of the photosensitivemembers 16Y, 16M, 16C, and 16K.

[0065] Each of the photosensitive members 16Y, 16M, 16C, and 16Kcomprises a photosensitive drum and a photosensitive layer formed on itssurface layer. They are uniformly charged by the charging means 17Y,17M, 17C, and 17K and are exposed to light thereafter so as to achieve alatent image formed according to the original image by means of each LDincluded in the original writing units 153Y, 153M, 153C, and 153K.

[0066] The developing devices 18Y, 18M, 18C, and 18K contain developerincluding yellow, magenta, cyan, and black toners, respectively. Eachdeveloping device is formed as a unit, thus the developing devicecontaining the developer is replaced with new one when the developer isexchanged. The developing devices 18Y, 18M, 18C, and 18K are controlledas to operation by the apparatus control CPU 101. The apparatus controlCPU 101 can manage their operating time as their usage histories and canstore the data into the nonvolatile memory 102. In addition, eachdeveloping device is provided with a sensor (not shown) for detecting anamount of remaining developer in the developing device. A result ofdetecting the amount is sent to the apparatus control CPU 101.

[0067] At the top of the image forming apparatus 1, there is provided anoriginal reading unit, which functions as the scanner unit 130. Anoriginal is set on its platen having a glass surface and then scannedand read by the original reading unit. The original reading unitcontains the CCD 131 for receiving an input of a reflected lightobtained by the scanning mentioned above. The original reading unit canbe provided with an automatic document feeder (ADF), though it is notshown in this diagram.

[0068] At the bottom of the image forming apparatus 1, there arearranged paper feed trays 12, 13, and 14, which are provided with paperfeeding means 12 a, 13 a, and 14 a, respectively. In addition, there isprovided a manual paper feed tray 15 on a lateral outer wall of theimage forming apparatus 1, with paper feeding means 15 a for the manualfeed tray 15. In this manner, there are provided a plurality of paperfeed trays and the manual paper feed tray, and therefore it is possibleto use a plurality of kinds of sheets different in size.

[0069] At the front of the paper feeding mechanism of the paper feedingmeans 12 a to 15 a, there is arranged a registration roller 25. Furtherahead of it there is arranged a secondary transfer roller 26 that canpush a sheet against the intermediate transfer member 19 a. Fixing means27 is provided ahead of the secondary transfer roller 26, and a paperdischarging roller 28 is provided ahead of the fixing means 27.Furthermore, it is also possible to arrange a stapling machine or otheroutput devices, not shown, in the discharging side of the paperdischarging roller 28.

[0070] In the image forming apparatus 1, the photosensitive members 16Y,16M, 16C, and 16K are charged by the charging means 17Y, 17M, 17C, and17K according to an image forming instruction from the apparatus controlCPU 101, and a given latent image is formed on the photosensitivemembers 16Y, 16M, 16C, and 16K according to the image data. Thedeveloping means 18Y, 18M, 18C, and 18K supply developer to thephotosensitive members 16Y, 16M, 16C, and 16K, by which the latent imageis visualized. The primary transfer means 19Y, 19M, 19C, and 19Ktransfer the image from the photosensitive members 16Y, 16M, 16C, and16K, where the image has been developed, to the intermediate transfermember 19 a. The developer remaining on the photosensitive members 16Y,16M, 16C, and 16K after the transfer is removed mechanically andelectrically by the cleaning units 20Y, 20M, 20C, and 20K, and it iscollected into a waste toner unit not shown. If the used developer doesnot need be classified at collection as in a black-and-white outputdevice, it can be disposed of directly as described above or can beturned into the developing device for reuse.

[0071] On the other hand, the sheet as a recording material necessaryfor the image formation is supplied by the paper feeding means 12 a, 13a, 14 a, or 15 a from one of the paper feed trays 12, 13, and 14 and themanual paper feed tray 15 according to a paper size determined based onprinting conditions or the like, and it reaches the secondary transferroller 26 via the registration roller 25. The secondary transfer roller26 pushes the sheet against the intermediate transfer member 19 a, bywhich the image on the intermediate transfer member 19 a is transferredto the sheet. The sheet having the transferred image takes image fixingprocessing by the fixing means 27 having a pair of heating rollers 27 a,27 a and then discharged to the outside of the image forming apparatus 1via the paper discharging roller 28. If the apparatus has apostprocessor such as a stapling machine, post-processing is performedif necessary. Upon completion of the image formation with the imageforming apparatus, the apparatus control CPU for controlling the imageforming apparatus updates the accumulated number of output sheets andthe apparatus operating time and stores them in the nonvolatile memory102.

[0072] In the image forming system, the image forming apparatus 1 isconnected to the plurality of image forming apparatuses 2 to n via theLAN 50 as shown in FIG. 1. Each of the image forming apparatuses 2 to ncomprises a control unit 100 as a body of a digital copier having aconfiguration equivalent to that of the image forming apparatus 1, ascanner unit 130, an operating unit 140, and an image processing controlunit 200.

[0073] The host device control computer 30 connected to the LAN 50 hasthe control unit 300 as mentioned above. The control unit 300 cancomprise a CPU not shown and a program for controlling it. The programcan be stored in a ROM (not shown) or the like in the control unit 300.The host device control computer 30 can communicate with other imageforming apparatuses via the LAN interface 30 a, and therefore it cantransmit or receive image data or image processing instructions to orfrom other image forming apparatuses. Furthermore, the control computer30 can make a request to other image forming apparatuses fortransmitting various usage history data, remaining developer amountdata, or average black ratio data stored in the image formingapparatuses at the time of output, and it can select output imageforming apparatuses according to a predetermined standard based on theabove data. A user can also control the contents of the selection afteran input of the image data by transmitting it to image formingapparatuses where the user is to input the data and displaying it on atouch panel of the image forming apparatuses.

[0074] While the independent host device control computer 30 isconnected separately from the image forming apparatuses and the hostdevice control unit 300 in the host device control computer 30 controlsthe output in this embodiment as stated above, it is also possible tocontrol the output by means of a host device control unit 300 a of aspecific or arbitrary image forming apparatus, which is included in theimage forming system as shown in FIG. 4. In this condition, the hostdevice control unit 300 a can comprise the apparatus control CPU 101 inthe image forming apparatus and a program for operating it. It is alsopossible that the host device control unit 300 a having a configurationequivalent to that of the host device control unit 300 is incorporatedin the image forming apparatus in the form of a substrate or the like soas to operate.

[0075] (Output Procedure 1)

[0076] The following describes a procedure for an output with theaforementioned image forming system by referring to FIG. 5.

[0077] One of the image forming apparatuses obtains image data byreading it from a scanner, determines output conditions (print settings,etc.), and starts an output operation (step I10). At that time, a usercan set the output conditions by means of the operating unit 140 in theimage forming apparatus 1. In addition, the user can select whether toenable the output. The output processing is started upon receiving thesecommand inputs and manually or automatically giving an instruction ofexecuting the output. The input image forming apparatus having startedthe output processing transmits the above output condition data andimage data to the host device control computer 30 (step I11). The hostdevice control computer 30, which has received the data via the LANinterface 30 a, receives an output request (step H10) and collates usagehistories of latent image carriers of the respective image formingapparatuses (step H11). If the image forming apparatuses are coloroutput devices, the collation of the usage histories can be intended forlatent image carriers for a specific color or it is possible toreference average data of a plurality of latent image carriers.

[0078] The host device control computer 30 can make inquires about theusage histories of the image forming apparatuses each time therewith andthey can respond to the inquiries of the host device control computer.Otherwise, the host device control computer can manage the usagehistories of the image forming apparatuses, store them in a nonvolatilememory, and read them out if necessary. The host device collates theabove usage histories and selects image forming apparatuses intended forthe output according to a predetermined standard (step H12). Thestandard can be, for example, a condition that the usage histories areapproximately the same in the image forming apparatuses. Afterdetermining the intended output devices, the host device controlcomputer sends a preparation request to the output image formingapparatuses, which are intended output devices. Upon receiving thepreparation request, the image forming apparatuses intended for theoutput prepare for the image output such as idling (step E10). Inaddition, with the determination of the intended output devices, thehost device control computer transmits information on the intendedoutput devices to the input image forming apparatus. The input imageforming apparatus displays the intended output device names on the touchpanel 141 of the operating unit 140 by means of the apparatus controlCPU 101, which has received the information on the intended outputdevices (I12). Furthermore, it awaits an input of an instruction ofexecuting the output with the display (step I13). If the executeinstruction is input during the awaiting, the execute instruction issent to the host device control computer. It is also possible to make anarrangement that the user can select a part of the image formingapparatuses required for the output out of the intended output devicesin the input of the execute instruction.

[0079] If the execute instruction is not input or the output is canceledin the above step I13, the series of procedure is terminated.Furthermore, it is also possible to cause an execute instruction to beautomatically made directly or under conditions that no input has beenmade for a given period of time or other conditions in step I13. Havingreceived the above output execute instruction, the host device controlcomputer 30 further transmits an instruction of executing the imageoutput, the image data to be output, and the output conditions to theintended output devices (selected intended devices if the input imageforming apparatus selects a part of the image forming apparatuses) (stepH13). Upon receiving the execute instruction, the image data, and theoutput conditions, the output image forming apparatuses execute theimage output according to the image data and the output conditions (stepE11). Completing the image output, the output image forming apparatusestransmit a notice of the completion to the host device control computer(step E12).

[0080] Upon receiving the notice of the output completion, the hostdevice control computer updates the usage histories of the latent imagecarriers of the image forming apparatuses having completed the imageoutput. If the host device control computer retains the usage historydata, it updates the data. If each image forming apparatus retains theusage history data, the host device control computer sends a request forupdating to the image forming apparatus. Otherwise, when the above imageoutput is completed, the output image forming apparatuses can update theusage histories without receiving the request from the host devicecontrol computer. After the completion of the image output, the hostdevice control computer further transmits a notice of the completion tothe input image forming apparatus. Upon receiving the notice, the inputimage forming apparatus displays an indication of the output completionon the display unit such as the touch panel or the like (step I14).

[0081] (Output Procedure 2)

[0082] The following describes another procedure for an output with theimage forming system by referring to FIG. 6.

[0083] The input image forming apparatus obtains image data, determinesoutput conditions (print settings, etc.), and starts the output (stepI20). In the same manner as for the above procedure, a user can set theoutput conditions or select whether to enable the output at that time.The output processing is started upon receiving these command inputs andmanually or automatically giving an instruction of executing the output.The input image forming apparatus having started the output processingtransmits the above output condition data and image data to the hostdevice control computer 30 (step I21). The host device control computer30, which has received the data, receives an output request (step H20)and collates usage histories of developer of the respective imageforming apparatuses (step H21). If the image forming apparatuses arecolor output devices, the collation of the usage histories can beintended for developer of a specific color or it is possible toreference average data of developer of a plurality of colors.

[0084] The host device control computer 30 can collect the usagehistories of the developer of the respective image forming apparatusesby inquiring of the image forming apparatuses each time or can store andmanage the usage histories of the developer of the image formingapparatuses. The host device collates the usage histories of thedeveloper and selects image forming apparatuses intended for the outputaccording to a predetermined standard (step H22). The standard can be,for example, a condition that the usage histories of the developer areapproximately the same in the image forming apparatuses. Afterdetermining the intended output devices, the host device controlcomputer sends a preparation request to the output image formingapparatuses, which are intended output devices. Upon receiving thepreparation request, the image forming apparatuses intended for theoutput prepare for the image output (step E20). Furthermore, with thedetermination of the intended output devices, the host device controlcomputer transmits information on the intended output devices to theinput image forming apparatus. The input image forming apparatusdisplays the intended output device names on the touch panel 141 (I22).Furthermore, it awaits an input of an instruction of executing theoutput with the display (step I23). If the execute instruction is inputduring the awaiting, the execute instruction is transmitted to the hostdevice control computer. It is also possible to make an arrangement thatthe user can select a part of the image forming apparatuses required forthe output out of the intended output devices in the input of theexecute instruction.

[0085] Furthermore, it is also possible to cause an execute instructionto be automatically made in step I23. Having received the above executeinstruction for the output, the host device control computer 30 furthertransmits an instruction of executing the image output, the image datato be output, and the output conditions to the intended output devices(selected intended devices if the input image forming apparatus selectsa part of the image forming apparatuses) (step H23). Upon receiving theexecute instruction, the image data, and the output conditions, theoutput image forming apparatuses execute the image output according tothe image data and the output conditions (step E21). Completing theimage output, the output image forming apparatuses transmit a notice ofthe completion to the host device control computer (step E22).

[0086] Upon receiving the notice of the output completion, the hostdevice control computer updates usage histories of the developer of theimage forming apparatuses having completed the image output. If the hostdevice control computer retains the usage history data, it updates thedata. If each image forming apparatus retains the usage history data,the host device control computer sends a request for updating to eachimage forming apparatus. Otherwise, when the above image output iscompleted, the output image forming apparatuses can update the usagehistories of the developer without receiving the request from the hostdevice control computer.

[0087] The usage history of the developer is automatically or manuallyreset by replacement of the developing device provided as a unit. Forexample, a target image forming apparatus resets the usage history. Ifthe host device control computer manages usage histories, the imageforming apparatus whose developing device was replaced transmits a resetinstruction to the host device control computer so that it can managethe usage histories appropriately.

[0088] After the completion of the image output, the host device controlcomputer further transmits a notice of the completion to the input imageforming apparatus. Upon receiving the notice, the input image formingapparatus displays an indication of the output completion on the touchpanel or other display units (step I24).

[0089] (Output Procedure 3)

[0090] The following describes still another procedure for an outputwith the image forming system by referring to FIG. 7.

[0091] The input image forming apparatus obtains image data, determinesoutput conditions (print settings, etc.), and starts the output (stepI30). In the same manner as for the above procedure, a user can set theoutput conditions or select whether to enable the output at that time.The output processing is started upon receiving these command inputs andmanually or automatically giving an instruction of executing the output.The input image forming apparatus having started the output processingtransmits the above output condition data and image data to the hostdevice control computer 30 (step I31). The host device control computer30, which has received the data, receives an output request (step H30)and collates usage histories (maintenance counters in this embodiment)of the respective image forming apparatuses after maintenance (stepH31). The maintenance counter indicates the number of output sheets ofrecording materials after the maintenance, and the counter value isreset to zero by carrying out the maintenance.

[0092] The host device control computer 30 can collect the maintenancecounter data of the respective image forming apparatuses by inquiring ofthe image forming apparatuses each time or can store and manage themaintenance counter data of the image forming apparatuses. The hostdevice collates the maintenance counter data and selects image formingapparatuses intended for the output according to a predeterminedstandard (step H32). The standard can be, for example, a condition thatthe maintenance counters indicate approximately the same value in theimage forming apparatuses. Otherwise, the standard can be a conditionthat the maintenance counters of the image forming apparatuses indicatevarious values, in other words, that the maintenance works do notconcentrate in the same period.

[0093] After determining the intended output devices, the host devicecontrol computer sends a preparation request to the output image formingapparatuses, which are intended output devices. Upon receiving thepreparation request, the image forming apparatuses intended for theoutput prepare for the image output (step E30). In addition, with thedetermination of the intended output devices, the host device controlcomputer transmits information on the intended output devices to theinput image forming apparatus. The input image forming apparatusdisplays the intended output device names on the touch panel 141 (I32).Furthermore, it awaits an input of an instruction of executing theoutput with the display (step I33). If the execute instruction is inputduring the awaiting, the execute instruction is transmitted to the hostdevice control computer. It is also possible to make an arrangement thatthe user can select a part of the image forming apparatuses required forthe output out of the intended output devices in the input of theexecute instruction.

[0094] Furthermore, it is also possible to cause an execute instructionto be automatically made in step I33. Having received the above executeinstruction for the output, the host device control computer 30 furthertransmits an instruction of executing the image output, the image datato be output, and the output conditions to the intended output devices(selected intended devices if the input image forming apparatus selectsa part of the image forming apparatuses) (step H33) Upon receiving theexecute instruction, the image data, and the output conditions, theoutput image forming apparatuses execute the image output according tothe image data and the output conditions (step E31). Completing theimage output, the output image forming apparatuses transmit a notice ofthe completion to the host device control computer (step E32).

[0095] Upon receiving the notice of the output completion, the hostdevice control computer updates the maintenance counters of the imageforming apparatuses having completed the image output. If the hostdevice control computer retains the maintenance counter data, it updatesthe data. If each image forming apparatus retains the maintenancecounter data, the host device control computer sends a request forupdating to each image forming apparatus. Otherwise, when the aboveimage output is completed, the output image forming apparatuses canupdate the maintenance counters without receiving the request from thehost device control computer.

[0096] The maintenance counter is reset at the maintenance carried outby a service person. For example, a target image forming apparatusresets the maintenance counter. If the host device control computermanages the maintenance counters, the image forming apparatus whosemaintenance was finished transmits a reset instruction to the hostdevice control computer so that it can manage the usage historiesappropriately.

[0097] After the completion of the image output, the host device controlcomputer further transmits a notice of the completion to the input imageforming apparatus. Upon receiving the notice, the input image formingapparatus displays an indication of the output completion on the displayunit such as the touch panel or the like (step I34).

[0098] (Output Procedure 4)

[0099] The following describes still another procedure for an outputwith the image forming system by referring to FIG. 8.

[0100] The input image forming apparatus obtains image data, determinesoutput conditions, and starts the output (step I40). In the same manneras for the above procedure, a user can set the output conditions orselect whether to enable the output at that time. The output processingis started upon receiving these command inputs and manually orautomatically giving an instruction of executing the output. The inputimage forming apparatus having started the output processing transmitsthe above output condition data and image data to the host devicecontrol computer 30 (step I41). The host device control computer 30,which has received the data, receives an output request (step H40) andcollates average photographic densities of the respective image formingapparatuses (step H41). A black ratio is defined as a ratio of an areaof a toner image to an area of an entire sheet. The average black ratioindicates an average of photographic densities after starting to use thedeveloper in the developing device provided as a unit. The black ratiodepends upon image data. Therefore, the average black ratio iscalculated every time an image is output. If the image formingapparatuses are color output devices, the calculation of the averagephotographic densities can be intended for developer of a specific coloror it is possible to reference average data of developer of a pluralityof colors.

[0101] The host device control computer 30 can collect the informationon the average photographic densities of the image forming apparatusesby inquiring of the image forming apparatuses each time or can store andmanage the information on the average photographic densities of theimage forming apparatuses. The host device collates the averagephotographic densities and selects image forming apparatuses intendedfor the output according to a predetermined standard (step H42). Thestandard can be, for example, a condition that the average photographicdensities are approximately the same in the image forming apparatuses.In this case, the image forming apparatuses for the output are selectedby calculating the black ratio of the image data intended for the imageoutput and calculating the average black ratio after outputting theimage based on an average black ratio of an already output image.

[0102] After determining the intended output devices, the host devicecontrol computer sends a preparation request to the output image formingapparatuses, which are intended output devices. Upon receiving thepreparation request, the image forming apparatuses intended for theoutput prepare for the image output (step E40). In addition, with thedetermination of the intended output devices, the host device controlcomputer transmits information on the intended output devices to theinput image forming apparatus. The input image forming apparatusdisplays the intended output device names on the touch panel 141 (I42)Furthermore, it awaits an input of an instruction of executing theoutput with the display (step I43). If the execute instruction is inputduring the awaiting, the execute instruction is transmitted to the hostdevice control computer. It is also possible to make an arrangement thatthe user can select a part of the image forming apparatuses required forthe output out of the intended output devices in the input of theexecute instruction.

[0103] Furthermore, it is also possible to cause an execute instructionto be automatically made in step I43. Having received the above executeinstruction for the output, the host device control computer 30 furthertransmits an instruction of executing the image output, the image datato be output, and the output conditions to the intended output devices(selected intended devices if the input image forming apparatus selectsa part of the image forming apparatuses) (step H43). Upon receiving theexecute instruction, the image data, and the output conditions, theoutput image forming apparatuses execute the image output according tothe image data and the output conditions (step E41). Completing theimage output, the output image forming apparatuses transmit a notice ofthe completion to the host device control computer (step E42).

[0104] Upon receiving the notice of the output completion, the hostdevice control computer updates the information on the averagephotographic densities of the image forming apparatuses having completedthe image output. If the host device control computer retains theinformation on the average photographic densities, it updates the data.If each image forming apparatus retains the information on the averagephotographic densities, the host device control computer sends a requestfor updating to each image forming apparatus. Otherwise, when the aboveimage output is completed, the output image forming apparatuses canupdate the information on the average photographic densities withoutreceiving the request from the host device control computer.

[0105] The information on the average black ratio is reset atreplacement of the developing device provided as a unit. For example, atarget image forming apparatus resets the information on the averageblack ratio. If the host device control computer manages the informationon the average photographic densities, the image forming apparatus whosedeveloping device has been replaced transmits a reset instruction to thehost device control computer so that it can manage the usage historiesappropriately.

[0106] After the completion of the image output, the host device controlcomputer further transmits a notice of the completion to the input imageforming apparatus. Upon receiving the notice, the input image formingapparatus displays an indication of the output completion on the displayunit such as the touch panel or the like (step I44).

[0107] (Output Procedure 5)

[0108] The following describes still another procedure for an outputwith the image forming system by referring to FIG. 9.

[0109] The input image forming apparatus obtains image data, determinesoutput conditions, and starts the output (step I50). In the same manneras for the above procedure, a user can set the output conditions orselect whether to enable the output at that time. The output processingis started upon receiving these command inputs and manually orautomatically giving an instruction of executing the output. The inputimage forming apparatus having started the output processing transmitsthe above output condition data and image data to the host devicecontrol computer 30 (step I51). The host device control computer 30,which has received the data, receives an output request (step H50) andcollates amounts of remaining developer of the respective image formingapparatuses (step H51). Furthermore, it calculates the black ratio ofthe image data in this procedure and predicts an amount of consumeddeveloper. If the image forming apparatuses are color output devices,the calculation of the photographic densities and the collation of theamounts of remaining developer can be intended for developer of aspecific color or it is possible to reference average data of developerof a plurality of colors.

[0110] The host device control computer 30 can collect the informationon the amount of remaining developer of each image forming apparatus byinquiring of the image forming apparatus each time or can store andmanage data of the amount of remaining developer of each respectiveimage forming apparatus using the host device control computer. The hostdevice collates the amounts of remaining developer and selects imageforming apparatuses intended for the output according to a predeterminedstandard (step H52). The standard can be, for example, a condition thatthe amounts of remaining developer after consumption are approximatelythe same in the image forming apparatuses. Depending upon the amounts ofremaining developer, it is possible to cause an image forming apparatushaving a small amount of remaining developer to be selectedpreferentially so that the developer is used up. Furthermore, it ispossible to predict an amount of consumed developer based on thecalculated black ratio of the image data and the number of output sheetsand then to set different selection standards for the selected imageforming apparatuses according the predicted amount of consumed developer(for example, a large or small amount). For example, if a large amountof developer is to be consumed, high-speed machines or machines eachhaving a large amount of remaining developer are selected.

[0111] After determining the intended output devices, the host devicecontrol computer sends a preparation request to the output image formingapparatuses, which are intended output devices. Upon receiving thepreparation request, the image forming apparatuses intended for theoutput prepare for the image output (step E50). In addition, with thedetermination of the intended output devices, the host device controlcomputer transmits information on the intended output devices to theinput image forming apparatus. The input image forming apparatusdisplays the intended output device names on the touch panel 141 (I52).Furthermore, it awaits an input of an instruction of executing theoutput with the display (step I53). If the execute instruction is inputduring the awaiting, the execute instruction is transmitted to the hostdevice control computer. It is also possible to make an arrangement thatthe user can select a part of the image forming apparatuses required forthe output out of the intended output devices in the input of theexecute instruction.

[0112] Furthermore, it is also possible to cause an execute instructionto be automatically made in step I53. Having received the above executeinstruction for the output, the host device control computer 30 furthertransmits an instruction of executing the image output, the image datato be output, and the output conditions to the intended output devices(selected intended devices if the input image forming apparatus selectsa part of the image forming apparatuses) (step H53). Upon receiving theexecute instruction, the image data, and the output conditions, theoutput image forming apparatuses execute the image output according tothe image data and the output conditions (step E51). Completing theimage output, the output image forming apparatuses transmit a notice ofthe completion to the host device control computer (step E52).

[0113] Upon receiving the notice of the output completion, the hostdevice control computer updates the remaining developer amount data ofthe image forming apparatuses having completed the image output. If thehost device control computer retains the remaining developer amountdata, it updates the data. If each image forming apparatus retains theremaining developer amount data, the host device control computer sendsa request for updating to each image forming apparatus. Otherwise, whenthe above image output is completed, the output image formingapparatuses can update the remaining developer amount data withoutreceiving the request from the host device control computer.

[0114] The remaining developer amount data is reset at replacement ofthe developing device provided as a unit. For example, a target imageforming apparatus resets the remaining developer amount data. If thehost device control computer manages the remaining developer amountdata, the image forming apparatus whose developing device has beenreplaced transmits a reset instruction to the host device controlcomputer so that it can manage the remaining developer amount dataappropriately.

[0115] After the completion of the image output, the host device controlcomputer further transmits a notice of the completion to the input imageforming apparatus. Upon receiving the notice, the input image formingapparatus displays an indication of the output completion on the displayunit such as the touch panel or the like (step I54).

[0116] The present invention has been described hereinabove inconnection with certain preferred embodiments.

[0117] According to the first aspect of the invention, the output imageforming apparatuses can be selected based on the usage history of alatent image carrier of each image forming apparatus. Therefore, outputdestinations can be determined according to conditions of the imageforming apparatuses different in frequency of use of their latent imagecarriers, thereby preventing a variance of an image quality caused bydifferences in conditions of the latent image carriers of the imageforming apparatuses.

[0118] The latent image carrier generally comprises a photosensitivedrum with an OPC, Se, or other photosensitive layer formed on itssurface. In the latent image carrier, a latent image is formed on auniformly charged surface by means of a laser beam. The latent image isdeveloped using developer and transferred to a recording material suchas paper. Thereafter, the latent image carrier is cleaned to removeremaining toner for a preparation for the next latent image. The aboveoperation is repeated in the latent image carrier. Therefore, itscharacteristic is gradually deteriorated by the repetitive useinevitably. The present invention enables the standardization of imagequalities of the respective image forming apparatuses by considering thedeterioration of the latent image carriers through use thereof.

[0119] In the present invention, the selection standard for the imageforming apparatuses based on the usage histories is, for example, acondition that the usage histories of the latent image carriers of theimage forming apparatuses are approximately the same. It is alsopossible to prevent a variance of an output quality by selecting imageforming apparatuses having similar usage histories.

[0120] If it is aimed to have approximately the same usage histories ofthe latent image carriers of the image forming apparatuses, outputdestinations can be selected so that the usage histories are graduallyconverged on approximately the same conditions through a plurality ofjobs, even if the usage histories of the image forming apparatuses arenot approximately the same at an output in a single job. By repeatingthe selection of the image forming apparatuses through the plurality ofjobs, approximately the same usage histories can be generated in theimage forming apparatuses. The standard for the usage histories of thelatent image carriers has only to be common in the image formingapparatuses, but it is not limited to specific one. The standard can bethe operating time of the latent image carriers or the number of sheetsto which an image is printed (transferred) based on a recordingmaterial. In other words, it only has to be useful for evaluating thecharacteristic of the latent image carrier deteriorating through use.

[0121] The usage history of the latent image carrier is intended for aspecific carrier. For example, the usage history is reset at replacementof the latent image carrier. There is a method of the reset in which aservice person manually resets the usage history at the replacement ofthe carrier or in which a fuse for detecting NEW is previously attachedto, for example, the latent image carrier to detect it automatically inthe image forming apparatus.

[0122] In some cases, the latent image carriers of the image outputdevices show various processes of performance changes (deterioration)through use due to differences of individual characteristics. Therefore,it is preferable to grasp the characteristic changes of the individuallatent image carriers previously and to select image output devicesbased on the usage histories after consideration of the characteristicchanges. For example, it is assumed that a latent image carrier a0 of animage output device A has a double tolerance for characteristic changesbased on the usage history in comparison with a latent image carrier b0of an image output device B. Supposing that the latent image carrier a0has a usage history of 15,000 sheets and the latent image carrier b0 hasa usage history of 10,000 sheets when the image output device A receivesa copy/printer command, the number of sheets as the usage history of thelatent image carrier b0 is lower than that of the latent image carriera0. Since the latent image carrier a0 has a double tolerance forcharacteristic changes based on the usage history, however, thecharacteristic of the latent image carrier a0 is equivalent to 7,500sheets (15,000 sheets divided by 2) in the characteristic of the latentimage carrier b0. Therefore, it is preferable to select the image outputdevice A in terms of an output quality in this case. While the aboveexample is illustrative only, as stated above it is possible to keep thelatent image carriers in approximately the same condition among theimage output devices by grasping various characteristic changes of thelatent image carriers for each model that may occur in connecteddifferent models and giving feedback to the selection of the imageoutput devices, thereby achieving similar output qualities even if theimage forming apparatuses have different functions. Additionally, in theabove condition, the usage history of each latent image carrier can bemodified based on the characteristic of deterioration through use ofeach latent image carrier. For example, a modified usage history isderived from a usage history not modified by showing a data table of arelation between the usage history not modified before consideration ofa characteristic difference between the latent image carriers and themodified usage history, making a graph of the relation, or defining acoefficient thereof. By selecting image forming apparatuses to which animage is output based on the modified usage histories, apparatuses moresuitable for actual conditions can be selected.

[0123] Subsequently, according to the fifth aspect of the invention,output image forming apparatuses are selected based on usage historiesof developer in respective image forming apparatuses. Therefore, outputdestinations can be determined according to conditions of the imageforming apparatuses different in frequency of use of their developer,thereby preventing a variance of an image quality caused by differencesin conditions of the developer of the image forming apparatuses.

[0124] The developer mainly comprises toner with plasticizer added ifnecessary. It is used for visualizing a latent image on the latent imagecarrier and is transferred as a toner image to a recording material asmentioned above. After the transfer, remaining toner on the latent imagecarrier is collected by cleaning and can be reused. Generally thedeveloping device contains the developer, and a required amount ofdeveloper is supplied from the developer to the latent image carrier bymeans of a developer conveying unit provided in the developing device.If the toner collected by cleaning is reused, the collected toner isreturned into the developing device. As mentioned above, the developeris gradually deteriorated by the developer conveying unit staying in theoperating developing device or through reuse of the developerinevitably. The present invention enables the standardization of imagequalities of the respective image forming apparatuses by considering thedeterioration of the developer through use thereof.

[0125] The selection standard for the image forming apparatuses based onthe usage histories is, for example, a condition that the usagehistories of the developer of the image forming apparatuses areapproximately the same. Otherwise, it is possible to prevent a varianceof an output quality by selecting image forming apparatuses havingsimilar usage histories.

[0126] If it is aimed to have approximately the same usage histories ofthe developer of the image forming apparatuses, output destinations canbe selected so that the usage histories of the developer of the imageforming apparatuses are approximately the same in an output in a singlejob, or they can be selected in such a way that the usage histories aregradually converged on approximately the same conditions. The standardfor the usage histories of the developer has only to be common in theimage forming apparatuses, but it is not limited to specific one. Thestandard can be the operating time of the developing device or thenumber of sheets to which an image is printed based on a recordingmaterial. In other words, it only has to be useful for evaluating thecharacteristic of the developer deteriorating through use.

[0127] The usage history of the developer is intended for a specificdeveloper. In many cases, developer is packaged with a developing deviceand the package is replaced when it is supplied in general. Therefore,the usage history is reset at replacement of developer. There is amethod of the reset in which a service person manually resets the usagehistory at the replacement of the developer or in which a fuse fordetecting NEW is previously attached to, for example, the developingdevice to detect it automatically in the image forming apparatus.

[0128] Furthermore, the developer of the image output devices showsvarious processes of performance changes (deterioration) depending onthe usage history due to differences of individual characteristics.Therefore, it is preferable to grasp the characteristics of thedeveloper in advance and to select image output devices based on theusage histories after consideration of the characteristic changes. Forexample, it is assumed that developer al of an image output device A hasa double tolerance for characteristic changes based on the usage historyin comparison with developer b1 of an image output device B. Supposingthat the developer a1 has a usage history of 15,000 sheets and thedeveloper b1 has a usage history of 10,000 sheets when the image outputdevice A receives a copy/printer command, the number of sheets as theusage history of the developer b1 is lower than that of the developera1. Since the developer a1 has a double tolerance for characteristicchanges based on the usage history, however, the characteristic of thedeveloper a1 is equivalent to 7,500 sheets (15,000 sheets divided by 2)in the characteristic of the developer b1. Therefore, it is preferableto select the image output device A in terms of an output quality inthis case. While the above example is illustrative only, as set forthabove it is possible to keep the developer in approximately the samecondition among the image output devices by grasping variouscharacteristic changes of the developer for each model that may occur inconnected different models and giving feedback to the selection of theimage output devices, thereby achieving similar output qualities even ifthe image forming apparatuses have different functions. In the abovecondition, the usage history of the developer can be modified based onthe characteristic of deterioration through use of the developer. Forexample, a modified usage history is derived from a usage history notmodified by showing a data table of a relation between the usage historynot modified before consideration of a characteristic difference of thedeveloper and the modified usage history, making a graph of therelation, or defining a coefficient thereof. By selecting image formingapparatuses to which an image is output based on the modified usagehistories, apparatuses more suitable for actual conditions can beselected.

[0129] Furthermore, according to the ninth aspect of the invention,output image forming apparatuses are selected based on usage historiesafter maintenance in respective image forming apparatuses. Therefore,output destinations can be determined according to conditions of theimage forming apparatuses depending on maintenance, thereby preventing avariance of an image quality caused by differences in conditions of theimage forming apparatuses.

[0130] In an image forming apparatus, an output quality graduallydeteriorates due to dirt or faulty adjustment of a mechanical system ina latent image carrier such as the aforementioned one, a laser beamoptical system for forming a latent image on the latent image carrier, afixing device for fixing toner by heating a recording material to whicha toner image is transferred, and a reading unit for reading an originalthrough continuous use of the apparatus. Therefore, most image formingapparatuses receive regular maintenance services (cleaning, mechanicaladjustment, etc.) conducted by a service person. The maintenance keepsthe output quality in a good condition. Thereafter, the characteristicis supposed to deteriorate gradually due to the gathering of dirtthrough continuous use. Therefore, the condition of an image formingapparatus can be known by grasping its usage history after themaintenance. The present invention enables the standardization of imagequalities or more efficient maintenance of the respective image formingapparatuses by considering the usage histories after maintenance.

[0131] Furthermore, it is possible to distribute the maintenance cyclesof the output image forming apparatuses intentionally in such a way thatmaintenance cycles of the respective models do not concentrate in thesame period. If the maintenance cycles concentrate in the same period,there may be a plurality of unavailable image output devices undermaintenance or characteristics of all image output devices may changeafter maintenance, thereby causing a noticeable change of the imagecharacteristics. In this manner, the maintenance cycles in the systemcan be set so as to come into the same period or be distributedintentionally according to the characteristic changes of the models orthe environment for use, thereby keeping optimum images appropriate forindividual usage.

[0132] The selection standard for the image forming apparatuses based onthe usage histories can be, for example, the operating time or thenumber of printed sheets based on the recording material of the imageforming apparatuses. In other words, it only has to be useful forevaluating the characteristics of the image forming apparatusesdeteriorating through use.

[0133] The usage history begins with a start of individual maintenance.Therefore, the usage history need be reset every time the maintenance iscarried out. It can be reset by a service person manually at themaintenance. Otherwise, it can be automatically reset at a detection ofan execution of the maintenance.

[0134] Furthermore, the image output devices show various processes ofperformance changes (deterioration) depending on the usage histories dueto differences of individual characteristics, thereby causing variousmaintenance cycles. Therefore, it is preferable to grasp thecharacteristics of the characteristics of deterioration through use ofthe image forming apparatuses in advance and to select image outputdevices based on the usage histories after consideration of thecharacteristic changes. This consideration enables a user to achieve thesimilar output qualities even if the image forming apparatuses aredifferent in functions. For example, it is assumed that a maintenancecycle A of an image output device A is twice as longer as a maintenancecycle B of an image output device B. Supposing that the image outputdevice A has a usage history of 200,000 sheets after maintenance and theimage output device B has a usage history of 150,000 sheets aftermaintenance when the image output device A receives a copy/printercommand, the number of sheets as the usage history after maintenance ofthe image output device B is lower than that of the image output deviceA. Since the maintenance cycle of the image output device A is twice aslonger as that of the image output device B, however, the characteristicof the image output device A is equivalent to 75,000 sheets (150,000sheets divided by 2) in the characteristic of the image output device B.Therefore, it is preferable to select the image output device A.

[0135] Furthermore, according to the 13th aspect of the invention,output image forming apparatuses are selected based on averagephotographic densities after replacements of developer. Therefore,output destinations can be determined according to conditions of theimage forming apparatuses depending on the average photographicdensities, thereby preventing a variance of an image quality caused bydifferences in conditions of the image forming apparatuses.

[0136] The black ratio is defined as a ratio of an area of a toner imageto an area of the entire sheet. In the present invention, the averageblack ratio can be calculated from black ratio data after replacement ofdeveloper and a usage history of developer.

[0137] Information data about the average black ratio is reset atreplacement of developer. There is a method of the reset in which aservice person manually resets it at replacement of developer or inwhich a fuse for detecting NEW is previously attached to, for example, alatent image carrier so that it is automatically detected in the imageforming apparatus.

[0138] In general, a high average black ratio indicates a large amountof consumed toner. Therefore, toner is exchanged frequently in adeveloping device. When toner remains in the developing device, itundergoes stress, thereby accelerating deterioration of toner.Therefore, as the average black ratio gets low, the characteristicchanges becomes large. It is preferable to select image output devicesso that the average photographic densities get close to the same valuein the respective image output devices. For example, it is assumed thatan image output device A has an average black ratio A of 15% and animage output device B has an average black ratio B of 30% when the imageoutput device A receives a copy/printer command. If the command receivedby the image output device A indicates 30% or higher, it is preferableto select the image output device A. If it indicates 15% or lower, it ispreferable to select the image output device B. If it indicates a valuebetween 15 to 30%, the average photographic densities are approximatelythe same in the image output devices in either case, and thereforeeither can be selected.

[0139] Still further, according to the 16th aspect of the invention,output image forming apparatuses are selected based on amounts ofremaining developer and a black ratio of image data in a job. Therefore,output destinations can be determined according to the amounts ofremaining developer after consumption and the amounts of remainingdeveloper of the image forming apparatuses can be controlled.

[0140] A high black ratio of an output image indicates a large amount ofconsumed toner. Therefore, it is possible to select image output devicesbased on the amounts of consumed toner and the amounts of remainingdeveloper so as to prevent the frequency of toner bottle replacements bya user (or a service person) from being nonuniform in the image outputdevices. Otherwise, if it is preferable to select and use image outputdevices having less remaining developer preferentially, the selection isconducted. For example, if a black ratio of an output image is low and asmall amount of image data is output, image output devices having lessremaining developer are selected preferentially. By using image outputdevices having a large amount of remaining developer when a large numberof image copies are output, it is possible to prevent a halt of theimage output caused by a lack of supplied toner during image outputoperation. More preferably, a certain amount of remaining developer canbe secured in favor of an image output device faster in an image outputin preparation for a large amount of output.

[0141] As described above, by selecting image output devices based onthe amount of remaining developer and the amount of consumed developerof each image output device, differences in performance of the imageoutput devices can be effectively used.

[0142] The image forming apparatus for use in the image forming systemof the present invention can be either of a black-and-white outputdevice and a color output device. The color output device has developerincluding color particles.

[0143] In the present invention, it is possible to cause an image outputautomatically in selected image forming apparatuses if the image formingapparatuses are selected based on usage histories or the like for theoutput. Otherwise, a user can specify image forming apparatuses for anoutput out of the selected image forming apparatuses. When an image isoutput from selected image forming apparatuses or specified imageforming apparatuses, the image can be output either automatically orafter awaiting an execute instruction from a user.

[0144] If output image forming apparatuses are selected based on theusage histories or the like as mentioned above, it can be noticed of auser by displaying names of the selected image forming apparatuses on adisplay unit. In addition, the display facilitates the specificationwork at the above specification.

[0145] The image forming apparatuses can be selected by an image formingapparatus as a host device after allocating an image forming apparatusdefined as a host device or an arbitrary image forming apparatus to ahost device. Otherwise, the host device control computer is providedindependently so that it can manage the image forming apparatuses.

[0146] Furthermore, all of the image forming apparatuses, which form theimage forming system, can be of the same model. In addition, at leastone image forming apparatus can be of a model different in functionsfrom other image forming apparatuses.

[0147] As set forth hereinabove, according to an image forming system ofthe present invention, it comprises communication means forinterconnection and a plurality of electrophotographic image formingapparatuses each visualizing a latent image on a latent image carriergenerated based on input image data by means of developer andtransferring it to a recording material, which are connected via thecommunication means, the image forming system having means for storingusage histories of the latent image carriers of the image formingapparatuses and having a function of selecting image forming apparatusesoutputting the image based on the carrier usage history data stored inthe storing means. Therefore, it becomes possible to achieveapproximately the same output image qualities in the printers bymanaging the usage histories so as to keep approximately the samedeteriorated conditions of the latent image carriers of the imageforming apparatuses.

[0148] According to another image forming system of the presentinvention, it comprises communication means for interconnection and aplurality of electrophotographic image forming apparatuses eachvisualizing a latent image on a latent image carrier generated based oninput image data by means of developer and transferring it to arecording material, which are connected via the communication means, theimage forming system having means for storing usage histories of thedeveloper of the image forming apparatuses and having a function ofselecting image forming apparatuses outputting the image based on thedeveloper usage history data stored in the storing means. Therefore, itbecomes possible to achieve approximately the same output imagequalities in the printers by managing the usage histories so as to keepapproximately the same deteriorated conditions of the developer of theimage forming apparatuses.

[0149] According to still another image forming system of the presentinvention, it comprises communication means for interconnection and aplurality of electrophotographic image forming apparatuses eachvisualizing a latent image on a latent image carrier generated based oninput image data by means of developer and transferring it to arecording material, which are connected via the communication means, theimage forming system having means for storing usage histories aftermaintenance of the image forming apparatuses and having a function ofselecting image forming apparatuses outputting the image based on theaforementioned usage history data. Therefore, it becomes possible toachieve approximately the same output image qualities in the printers bymanaging the usage histories after maintenance so that maintenancecycles of the image forming apparatuses complete at approximately thesame time. Furthermore, it has an advantage that the maintenance can becarried out at a time.

[0150] According to still another image forming system of the presentinvention, it comprises communication means for interconnection and aplurality of electrophotographic image forming apparatuses eachvisualizing a latent image on a latent image carrier generated based oninput image data by means of developer and transferring it to arecording material, which are connected via the communication means, theimage forming system having means for calculating and storing averagephotographic densities of developer after replacement and having afunction of selecting image forming apparatuses outputting the imagebased on the average black ratio data stored in the storing means.Therefore, it becomes possible to achieve approximately the same outputimage qualities in the printers by calculating the average photographicdensities of the printed image data of the developer from the usagehistories of the developer and managing the average photographicdensities.

[0151] According to still another image forming system of the presentinvention, it comprises communication means for interconnection and aplurality of electrophotographic image forming apparatuses eachvisualizing a latent image on a latent image carrier generated based oninput image data by means of developer and transferring it to arecording material, which are connected via the communication means, theimage forming system having means for detecting amounts of remainingdeveloper of the image forming apparatuses and means for calculating ablack ratio of the image data and having a function of selecting imageforming apparatuses outputting the image based on the remainingdeveloper amount data and the black ratio data. Therefore, it becomespossible to control the amounts of remaining developer to beapproximately the same in the printers or to control one side ofprinters to consume a large amount of developer by managing theremaining developer amount data and the black ratio data.

What is claimed is:
 1. An image forming system comprising: communicationmeans for interconnection; and a plurality of electrophotographic imageforming apparatuses each visualizing a latent image on a latent imagecarrier generated based on input image data by means of developer andtransferring the visualized image to a recording material, which areconnected via said communication means; the image forming system havingmeans for storing usage histories of the latent image carriers of theimage forming apparatuses and having a function of selecting imageforming apparatuses outputting the image based on the carrier usagehistory data stored in said storing means.
 2. The image forming systemaccording to claim 1, wherein the usage history of said latent imagecarrier is based on the number of transferred pages obtained withreference to an operating time or recording materials.
 3. The imageforming system according to claim 1, wherein the usage history of saidlatent image carrier is modified according to a characteristic ofdeterioration through use of each latent image carrier.
 4. The imageforming system according to claim 1, wherein the image formingapparatuses outputting the image are selected so that the usagehistories of the latent image carriers of the image forming apparatusesare approximately the same.
 5. An image forming system comprising:communication means for interconnection; and a plurality ofelectrophotographic image forming apparatuses each visualizing a latentimage on a latent image carrier generated based on input image data bymeans of developer and transferring the visualized image to a recordingmaterial, which are connected via said communication means; the imageforming system having means for storing usage histories of the developerof the image forming apparatuses and having a function of selectingimage forming apparatuses outputting the image based on the developerusage history data stored in said storing means.
 6. The image formingsystem according to claim 5, wherein the usage history of the developeris based on the number of transferred pages obtained with reference toan operating time of a developing device, which contains the developerand supplies it to the latent image carrier, or recording materials. 7.The image forming system according to claim 5, wherein the usage historyof the developer is modified according to a characteristic ofdeterioration through use of the developer.
 8. The image forming systemaccording to claim 5, wherein the image forming apparatuses outputtingthe image are selected so that the usage histories of the developer areapproximately the same in the image forming apparatuses.
 9. An imageforming system comprising: communication means for interconnection; anda plurality of electrophotographic image forming apparatuses eachvisualizing a latent image on a latent image carrier generated based oninput image data by means of developer and transferring the visualizedimage to a recording material, which are connected via saidcommunication means; the image forming system having means for storingusage histories after maintenance of the image forming apparatuses andhaving a function of selecting image forming apparatuses outputting theimage based on the usage history data.
 10. The image forming systemaccording to claim 8, wherein the usage history after maintenance isbased on the number of transferred pages obtained with reference to anoperating time for image formation of the image forming apparatus orrecording materials.
 11. The image forming system according to claim 9,wherein the usage history after maintenance is modified according to acharacteristic of deterioration through use of each image formingapparatus.
 12. The image forming system according to claim 9, whereinthe image forming apparatuses outputting the image are selected so thatthe usage histories after maintenance are approximately the same in theimage forming apparatuses.
 13. An image forming system comprising:communication means, for interconnection; and a plurality ofelectrophotographic image forming apparatuses each visualizing a latentimage on a latent image carrier generated based on input image data bymeans of developer and transferring the visualized image to a recordingmaterial, which are connected via said communication means; the imageforming system having means for storing information on averagephotographic densities of developer after replacement and having afunction of selecting image forming apparatuses outputting the imagebased on the average photographic densities obtained from theinformation.
 14. The image forming system according to claim 13, whereinthe means for storing the information on the average photographicdensities includes at least means for storing usage histories of thedeveloper, means for calculating the photographic densities during imageformation successively, and means for calculating the averagephotographic densities from the usage histories and the successivelycalculated photographic densities.
 15. The image forming systemaccording to claim 13, wherein the image forming apparatuses outputtingthe image are selected so that the average photographic densities areapproximately the same in the image forming apparatuses.
 16. An imageforming system comprising: communication means for interconnection; anda plurality of electrophotographic image forming apparatuses eachvisualizing a latent image on a latent image carrier generated based oninput image data by means of developer and transferring the visualizedimage to a recording material, which are connected via saidcommunication means; the image forming system having means for detectingamounts of remaining developer of the image forming apparatuses andmeans for calculating a black ratio of the image data and having afunction of selecting image forming apparatuses outputting the imagebased on the remaining developer amount data and the black ratio data.17. The image forming system according to claim 16, wherein the imageforming apparatuses outputting the image are selected so that theamounts of remaining developer after the image formation areapproximately the same in the image forming apparatuses.
 18. The imageforming system according to claim 1, wherein the developer containscolor particles.
 19. The image forming system according to claim 1,wherein a part or all of the plurality of image forming apparatusesconnected to each other via said communication means are of differentmodels.
 20. The image forming system according to claim 1, furthercomprising a display unit for displaying a list of the image formingapparatuses selected for outputting the image.
 21. The image formingsystem according to claim 20, further comprising an operating unit forgiving an instruction to execute the output with specifying a part orall of the image forming apparatuses displayed on said display unit. 22.The image forming system according to claim 1, further comprising a hostdevice control unit for selecting the image forming apparatusesoutputting the image based on one of the data.
 23. The image formingsystem according to claim 22, wherein said host device control unit isincorporated in at least one of the image forming apparatuses.
 24. Theimage forming system according to claim 22, wherein said host devicecontrol unit is connected to said image forming apparatusesindependently of the image forming apparatuses connected to each other.